At the present time, all car-plate identification systems are fixed types which are installed at fixed spots. All of these systems are provided with a sensing unit to detect a car that passed thereby. The sensing unit will trigger a photographing apparatus to identify a car-plate. Such a fixed type car-plate identification system has to be installed at a suitable spot and requires a considerable constuction work after it is set up, such system can only conduct a sensing operation and a photographing operation at a given angle over a limited area. It cannot perform a mobile identification operation of a car-plate to be placed on a car under moving condition so as to detect a stolen or otherwise wanted car. In other words, it has no mobility. Such type of identification system comprises several photo-sensitive detectors to detect a car passing a given spot, and to send a photographing instruction to allow a camera take a car-plate image, which is transmitted into an image-processing unit to find the position of a car-plate by means of a differential space frequency (i.e. intensity) analysis method. The outer frame of a car-plate is to be defined by means of a projection method, and then each character of a car-plate is extracted by means of a differential limiting-value analysis method; each character of a car-plate is then identified by means of a gray-scale three code method or an template-matching method.
In the aforesaid prior art, a projection method is used for extracting the characters of a car-plate. In case of a car-plate being a smaller one or being smeared, a wrong character extraction might occur, causing a wrong identification. Moreover, the prior art is unable to identify the characters of a car-plate in the event of the character being deformed or smeared.